Opposition to the Umayyads
finally came to a head in northeastern Iran (Khorasan) in 747
when the mawla Abu Muslim raised black banners
in the name of the 'Abbasids, a branch of the
family of the Prophet, distantly related to 'Ali and his
descendants. In 749 the armies from the east reached Iraq, where
they received the support of much of the population. The
'Abbasids themselves came from their retreat at Humaymah
in southern Jordan, and in 749 the first 'Abbasid caliph, as-Saffah,
was proclaimed in the mosque at Al-Kufah.

This " 'Abbasid Revolution"
ushered in the golden age of medieval Iraq. Khorasan
was too much on the fringes of the Muslim world to be a suitable
capital, and from the beginning the 'Abbasid caliphs made Iraq
their base. By this time Islam had spread well beyond the
original garrison towns, even though Muslims were still a
minority of the population.

At first the 'Abbasids ruled from Al-Kufah
or nearby, but in 762 al-Mansur founded a new
capital on the site of the old village of Baghdad.
It was officially known asMadinat as-Salam ("City of Peace"), but in popular
usage the old name prevailed. Baghdad soon became larger than any
city in Europe or western Asia. Al-Mansur built the massive Round
City with four gates and his palace and the main mosque in the
centre. This Round City was exclusively a government quarter, and
soon after its construction the markets were banished to the Karkh
suburb to the south. Other suburbs soon grew up,
developed by leading courtiers: Harbiyyah to the
northeast, where the Khorasani soldiers were settled, and, across
the Tigris on the east bank, a new palace quarter for the
caliph's son and heir al-Mahdi.

The siting of Baghdad
proved to be an act of genius. It had access to both the Tigris
and Euphrates river systems and was close to the
main route through the Zagros Mountains to the Iranian
plateau. Wheat and barley from Al-Jazirah
and dates and rice from Basra and the south
could be brought by water. By the year 800 the city may have had
as many as 500,000 inhabitants and was an important commercial
centre as well as the seat of government. The city grew at the
expense of other centres, and both the old Sasanian capital at Ctesiphon
(called Al-Mada'in, "The Cities," by the Arabs) and the
early Islamic centre at Al-Kufah fell into
decline.

The high point of prosperity was
probably reached in the reign of Harun ar-Rashid
(786-809), when Iraq was very much the centre of the empire and
riches flowed into the capital from all over the Muslim world.
The prosperity and order in the southern part of the country was,
however, offset by outbreaks of lawlessness in Al-Jazirah,
notably the rebellion of the Bedouin Walid ibn Tarif,
who defied government forces between 794 and 797. Even the most
powerful governments found it difficult to extend their authority
beyond the limits of the settled land.

Much more serious disruption followed
the death of Harun in 809. He left his son al-Amin
as caliph in Baghdad but divided the Caliphate and gave his son al-Ma'mun
control over Iran and the eastern half of the empire. This
arrangement soon broke down, and there ensued a prolonged and
very destructive civil war. The supporters of al-Amin made an
ill-judged attempt to invade Iran in the spring of 811 but were
soundly defeated at Rayy (modern Shahr-e Rey,
just south of modern Tehran). Al-Ma'mun's supporters retaliated
by invading Iraq, and from August 812 until September 813 they
laid siege to Baghdad, while the rest of Iraq slid into anarchy.
The collapse of Baghdadi resistance and the death of al-Amin did
not improve matters, for al-Ma'mun, now generally recognized as
caliph, decided to rule from Marw in distant Khorasan
(modern Mary, in Turkmenistan).This downgrading of Iraq
united many different groups in prolonged and bitter resistance
to al-Ma'mun's governor and led to another siege of Baghdad.
Finally al-Ma'mun was forced to concede that he could not rule
from a distance, and in August 819 he returned to Baghdad.

Once again Iraq was the central province
of the Caliphate and Baghdad the capital, but the prolonged
conflict had left much of Baghdad in ruins and caused great
destruction in the countryside. It probably marked the beginning
of the long decline in the prosperity of the area; this decline
was marked from the 9th century onward. Al-Ma'mun
sent his generals to bring Syria and Egypt
back under 'Abbasid rule and set about restoring the government
apparatus, many of the administrative records having been
destroyed in the fighting. His reign in Baghdad (819-833) saw
Iraq become the centre of remarkable cultural activity, notably
the translation of Greek science and philosophy into Arabic. The
caliph himself collected texts, employed translators like the
celebrated Hunayn ibn Ishaq, and established an
academy in Baghdad, the Bayt al-Hikmah
("House of Wisdom"), with a library and an observatory.
Private patrons such as the Banu Musa brothers
followed his example. This activity had a profound effect not
only on Muslim intellectual life but also on the intellectual
life of western Europe, for much of the science and philosophy
taught in universities in the Middle Ages was derived from these
Arabic translations, rendered into Latin in Spain
in the 12th century.

Politically the position was less rosy.
Al-Ma'mun was unable to recruit sufficient forces to replace the
old 'Abbasid army that had been destroyed in the civil war, and
he became increasingly dependent on his younger brother, Abu
Ishaq, who had gathered a small but highly efficient
force of Turkish mercenaries, many of them
slaves or ex-slaves from Central Asia. When al-Ma'mun died in
833, Abu Ishaq, under the title of al-Mu'tasim,
succeeded him without difficulty. Al-Mu'tasim was no intellectual
but rather an effective soldier and administrator. His reign
marks the introduction into Iraq of an alien, usually Turkish,
military class, which was to dominate the political life of the
country for centuries to come. From this time Iraqi Arabs were
rarely employed in military positions, though they continued to
be influential in the civil administration.

The recruitment of this new military
class provoked resentment among the Baghdadis, who felt that they
were being excluded from power. This resentment led al-Mu'tasim
to found a new capital at Samarra', the last
major urban foundation in Iraq until the 20th century. He chose a
site on the Tigris about 100 miles north of Baghdad. Here he laid
out a city with palaces and mosques, broad straight streets, and
a regular pattern of housing. The ruins of this city, which was
expanded by his successor al-Mutawwakil
(847-861), can still be seen on the ground and, more strikingly,
in aerial photographs, in which the whole plan can be made out.
Samarra' became a vast city, but it had none of the natural
advantages of Baghdad: communication by river and canal with the
Euphrates and southern Iraq was much more difficult, and despite
massive investment the water supply was always inadequate.
Samarra' survived only while it was the capital of the Caliphate,
from 836 to 892. When the caliphs returned to Baghdad, it showed
no independent urban vitality and soon shrank to a small
provincial town, which is why its remains can still be seen when
all traces of early 'Abbasid Baghdad have disappeared.

For nearly 30 years the new regime
worked well, and Iraq was for the last time the centre of a large
empire. Tax revenues from other areas enriched Samarra', and
Baghdad continued to prosper under the rule of the Tahirid
family. Basra remained a great entrepÔt on the Persian Gulf. The
employment of Turkish soldiers without any ties to the local
community gave rise to political instability, however. In 861 the
caliph al-Mutawwakil was assassinated in his
palace in Samarra' by disaffected troops, and there began a
nine-year anarchy in which the Turkish soldiers made and deposed
caliphs virtually at will. In 865 open civil war raged between
Samarra' and Baghdad, resulting in another destructive siege of
Baghdad. The anarchy played itself out, and in 870 stability was
restored with the caliph al-Mu'tamid in Samarra'
as titular ruler and his dynamic military brother al-Muwaffaq
exercising real power in Baghdad, but the anarchy had done real
and lasting damage to Iraq. Almost all the provinces of the
empire, both the Iranian lands in the east and Syria
and Egypt to the west, had broken away and
become independent. Worse, a major social revolt had broken out
in southern Iraq itself. In the prosperous years of early Islamic
Iraq, large numbers of slaves had been imported from East Africa
to be used in grueling agricultural work in the marshes of
southern Iraq. In 869 they rose in rebellion, led by an Arab who
claimed to be a descendant of 'Ali. This rebellion was extremely
serious for the 'Abbasid government: it laid to waste large areas
of agricultural land, and the great trading port of Basra was
taken and sacked in 871, the rebels burning mosques and houses
and massacring the inhabitants with indiscriminate ferocity.
Although Basra was soon recaptured, it is unlikely that it ever
fully recovered, and trade shifted down the gulf to cities such
as Siraf (modern Taheri) in southern Iran. The
crushing of this revolt involved long and hard amphibious
campaigns in the marshes, led by al-Muwaffaq and
his son Abu' l-'Abbas (later the caliph al-Mu'tathid)
from 879 until the rebel stronghold at Mukhtarah
was finally taken in 883.

The reigns of al-Mu'tathid
(892-902) and his son al-Muktafi (902-908) saw
Iraq united under 'Abbasid control. Once more Baghdad
was the capital, although the caliphs had largely abandoned the
Round City of al-Mansur on the west bank, and the centre of
government now lay on the east bank in the area that has remained
the centre of the city ever since. It was a period of great
cultural activity, and Baghdad was home to many intellectuals,
including the great historian at-Tabari, whose
vast work chronicled the early history of the Muslim state;
however, it was no longer the capital of a great empire. During
the reign of the boy caliph al-Muqtadir
(908-932), the political situation deteriorated rapidly. The
weakness of the caliph gave rise to endless intrigues among
parties of viziers and to a growing tendency for the military to
take matters into its own hands. Increasingly the government in
Baghdad lost control of the revenues and lands of Iraq. In 935
the final crisis occurred when the caliph ar-Rai
was obliged to hand over all real secular power to an ambitious
general, Ibn Ra'iq.

The political catastrophe of the
'Abbasid Caliphate was accompanied by economic collapse. It is
probable that the vicious circle of decline started with the
civil war after Harun's death in 809, and there
can be no doubt that it was exacerbated by the demands of the Turkish
military for payment. Administrators increasingly resorted to
short-term expedients such as tax farming, which encouraged
extortion and oppression, and the granting of iqtas
to the military. In theory, iqta's were grants
of the right to collect and use tax revenues; they could not be
inherited or sold. The purpose of an iqta' was
that the soldiers themselves would collect what they could
directly from lands assigned to them. Both these remedies put a
premium on short-term exploitation of land rather than long-term
investment. Except in the north, most Iraqi agriculture was
dependent on investment in and upkeep of complex irrigation
works, and these new fiscal systems proved disastrous. In 935,
the same year in which ar-Rai handed over power
to the military leader Ibn Ra'iq, the greatest
of the ancient irrigation works of central Iraq, the Nahrawan
canal, was breached to impede an advancing army. The
damage was never repaired, large areas went out of cultivation,
and villages were abandoned. The destruction of the canal is
symbolic of the end of the irrigation culture that had brought
great wealth to ancient Mesopotamia and that had
underpinned Sasanian and early Islamic government.